1. Field of the Invention
The present invention relates to a marine engine. More particularly, preferred embodiments provide an improved air induction system for a marine engine that reduces noise.
2. Description of the Related Art
Personal watercraft are designed to be relatively small and maneuverable, and are usually capable of carrying one, to three riders. These craft commonly include a relatively small hull that defines a rider's area above an engine compartment. The rider's area normally includes a seat.
The engine compartment contains an internal combustion engine that powers a jet propulsion unit. The jet propulsion unit, which includes an impeller, is positioned within a tunnel formed on an underside of the hull behind the engine compartment. A shaft, which is driven by the engine, usually extends between the engine and the jet propulsion device through a bulkhead of the hull tunnel.
The engine includes an air induction system for delivering air into one or more combustion chambers. The engine also includes an exhaust system for expelling exhaust gases from the combustion chambers to the body of water in which the watercraft operates. Where four-cycle engines are used, air enters the combustion chambers through intake valves, and exhaust gases exit the combustion chambers through exhaust valves.
In some four-cycle engines, the valve drive is configured such that the intake valves begin to open just before the end of the exhaust stroke, i.e., just before the piston reaches top dead center. As a result, a small amount of exhaust gas is pushed through the intake valves. This phenomenon is commonly referred to as intake blow back.